U.S. Pat. No. 6,083,001 describes an apparatus for accurate control of particles flow with regard to feeding abrasive material to a surface of teeth during dental treatment. The apparatus comprises a compressor for establishing a flow of pressurised air, a chamber for mixing the pressurised air and the particles of abrasive material and a hand piece for letting out the mixture of pressurised air and abrasive material onto the surface of the teeth, which are to be treated. The chamber for mixing the pressurised air and the particles of abrasive material has an inlet for pressurised air, said inlet being situated in an outlet for the abrasive material at a level below a top level of abrasive material in the chamber. Thus, the mixing of pressurised air and particles of abrasive material takes place directly at the outlet of the abrasive material towards the hand piece.
This, however, has the disadvantage that the mixing of the pressurised air and the particles of abrasive material only has very little time and very little space during which and in which the mixing can take place. This results in either an unsatisfactory mixing and/or a very uneven mixing of the pressurised air and the particles of abrasive material.
U.S. Pat. No. 6,004,191 describes a hand piece where mixing of pressurised air and particles of abrasive material takes place in a chamber in the hand piece itself and where a fluidisation of the particles of abrasive material is established during mixing. The pressurised air is let into the chamber along a tube extending from one end towards another end of the chamber and with an orifice directed towards the other end. The mixed pressurised air and particles of abrasive material are let out of the chamber through another tube extending from a position in the middle of the chamber and towards and out through the other end of the chamber. This apparatus ensures a mixing which fluidises the particles of abrasive material.
However, still the mixing may be unsatisfactory or may be very unequal due to the pressurised air being let towards the other end of the chamber. This results in the mixing being very dependent on the amount of particles of abrasive material which is present in the chamber, and also being very dependent on the inclination of the chamber and thus where in the chamber that the particles of abrasive material is situated.
U.S. Pat. No. 4,482,322 describes a device for mixing an abradant with pressurised gas. The device comprises a reservoir for the abradant and a separate vortex chamber for mixing the abradant and the pressurised gas. An inlet in the vortex chamber is provided tangentially to the circumference of the chamber so that air flowing into the vortex chamber is swirled in a controlled manner. Thereby a favourable swirling of the abradant is obtained. An orifice is provided in the bottom of the reservoir, and the abradant is thus intended, by means of gravity, for trickling down into the vortex chamber through the orifice. The trickling down is provided by vibrating the reservoir.
As mentioned, the device comprises a reservoir for containing the abradant and a separate vortex chamber for mixing the abradant with pressurised gas just before being used for surface treatment of teeth. For passing the abradant to the vortex chamber through the orifice, means has to be provided for vibrating the reservoir. This makes the device expensive and technically complicated and increases the need for regulation and adjustment means for obtaining correct dosage of the abradant and correct mixing of the abradant with the pressurised gas.
It is an object of the present invention to provide an apparatus, which ensures not only a satisfactory mixing of pressurised air and particles of abrasive material, but which also ensures a very equal distribution of the particles in the air so that a thorough and uniform abrasive treatment of the surfaces of teeth may be obtained together with an apparatus not comprising technically complicated and economically cost increasing means.